The dice and nature of RNG
The D20 as a probability distribution, have a linear distribution of outcome, with average values having equal chances of showing up as extreme values have.
Other systems include dice pools and success count ups, these systems have a high variance in potential.
D100 which tend to deal more in margins of success and failure rather than simply success or failure.
I would personally prefer a D20 difficulity scale for the roll outcomes changed from roll 1d20 roll to 3d6 , either as a default or as a option that in normally is considered take 10.